The recent availability of an entirely new gamma ray sensing material makes it possible to develop a new nuclear imager for early detection of breast cancer. This small, lightweight imager may be inserted in the position of a conventional mammography film plate to provide close registration of nuclear image and mammogram. It may also be placed at other locations such as the axilla to search for metastases Recent investigations indicate that the use of such an instrument in patients injected with an appropriate radioactive agent will improve the detection of malignancies and the ability to differentiate benign and malignant abnormalities in the breast. The new sensing material resulted from recent research in crystal growth and detector manufacturing technology by this company. The primary Phase I goal is to fabricate a cd2 x 2 cm imager, including sensing element and electronics. This will operate as a miniature imager for use in demonstrating feasibility of the overall approach and establishing parameters for a Phase II manufacturing prototype. Phase I parameters to address include optimal dimensionality of the imaging sensor, operating voltages, and collimator configuration.